1. Technical Field
The present invention relates to a combustion chamber of an internal combustion engine of the type having two combustion chambers, i.e., a main and auxiliary combustion chamber, and more particularly to an auxiliary combustion chamber or a so-called swirl chamber in which a swirl is generated and primary combustion takes place.
2. Background Art
Many diesel engines have main and auxiliary combustion chambers, and in some of such engines the auxiliary combustion chamber is a swirl chamber. In a diesel engine having a main combustion chamber and a swirl chamber, the intake air is pushed into the swirl chamber at the compression stroke of the engine, and fuel sprayed from a nozzle is mixed with air swirling in the swirl chamber and then a precombustion or primary combustion takes place therein.
Referring to FIG. 4 of the accompanying drawings, the main combustion chamber 2 is defined by a recess formed in the piston 1 top and the swirl chamber 4 is defined by a cavity formed in the cylinder head 3. The swirl chamber 4 communicates with the main combustion chamber 2 via a passage 6 formed in the cylinder head 4 when the piston 1 is at or near top dead center. A part of the passage 6 defines a tangential line of the wall defining the swirl chamber 4. During the compression stroke of the piston, the intake valve 7 is closed and the air sucked in the main combustion chamber 2 is forced into the swirl chamber 4, whereby a swirl of certain strength occurs in the swirl chamber 4. During the combustion process, fuel supplied from the nozzle 8 is ignited by a glow plug 9 or self-ignited (primary combustion) in the swirl chamber 4, and then the combustion gas therein proceeds to the main combustion chamber 2 via the passage 6 whereby a secondary combustion takes place in the main chamber 2.
The air utilization factor in the swirl chamber 4 becomes better as the swirl flows faster. Therefore, better combustion can be expected as the swirl speed becomes higher. In this aspect, attention in the past had primarily focused on the passage 6 between the main and auxiliary combustion chambers. Typical modifications are: (1) to throttle the passage 6 to a certain extent and (2) to change the direction of extension of the passage 6. In either case, however, friction loss is inevitable since the air 6 is throttled through the passage 6 in the former case, and the air does not rotate in the swirl chamber 4 smoothly in the latter case. Such friction loss results in deceleration of the swirl, which in turn results in poorer combustion.